In recent years, portable terminals used for mobile communication have been increasingly reduced in size and been made multi-banded to be able to handle a plurality of communication systems. Further, the portable terminals have been given more functions. Therefore, the built-in circuits have increased. For this reason, as the individual electronic parts used, for improvement of their mounting density, surface mountable small-size parts are being strongly demanded.
Among such electronic parts, there are the acoustic wave devices—used as the key parts of portable terminals. Acoustic wave devices include, for example, surface acoustic wave devices constituted by a piezoelectric substrate on which excitation electrodes are formed and thin film bulk acoustic resonators constituted by a thin piezoelectric film sandwiched between electrodes.
In the surface acoustic wave devices, to meet with the above demands for smaller size, the WLP (wafer level package) type has been proposed (for example, Patent Literature 1).
FIG. 15 is a cross-sectional view of principal parts schematically showing a surface acoustic wave device of the WLP type. As shown in FIG. 15, this surface acoustic wave device 101 is provided with a piezoelectric substrate 102 on one major surface of which excitation electrodes 103 are disposed and a sealing member 105 disposed on the piezoelectric substrate 102. More specifically, on the piezoelectric substrate 102, a protective film 104 covering the excitation electrodes 103 is disposed. The sealing member 105 is provided with a frame-shaped part 105a surrounding the excitation electrodes 103 and a lid part 105b disposed on the frame-shaped part 105a. Between the protective film 104 and the frame-shaped part 105a, an intermediate layer 106 joining these is disposed. By such a constitution, a space is formed between the excitation electrodes 103 covered by the protective film 104 and the lid part 105b. This space is tightly sealed by the sealing member 105. By performing this, invasion of moisture etc. in the atmosphere into the space inside this sealing member 105 is suppressed, and corrosion of the excitation electrodes 103 is suppressed.
In this regard, the surface acoustic wave device 101 is subjected to external force at the time of being diced from a wafer in a production process, at the time of washing in a mounting process, or at the time of use after mounting etc. Accordingly, peeling sometimes occurs between the sealing member 105a and an intermediate layer 106, so there was the problem of a decline in the airtight property of the space inside the sealing member 105.
The present invention was made in order to solve the above problem and has as an object thereof to provide an acoustic wave device able to suppress peeling of the sealing member and improve the airtight property of a space inside a sealing member.